1. Field of the Invention
This invention relates to a color printer for making copied prints from original color pictures.
2. Description of the Prior Art
It is generally known from experience that, in a regular photographic scene, the average reflection powers of blue, green and red, which are obtained by integrating the photographic scene as a whole, are substantially constant. Accordingly, in a conventional color printer, a copied print having a high color balance and a reasonable degree of printing is made by a gray integration printing method, in which the amounts of transmitted light of blue, green and red colors of an original color picture are measured to control the exposure, which is applied to blue, green and red color-sensitive layers of a photosensitive copying medium (mainly, color paper), to a constant level on the basis of the amounts determined in the mentioned measurement.
When the above method is used, high-quality copied prints can be made from most of the various original color pictures. In order to make such high-quality copied prints, it is necessary that the standard copying conditions in a color printer for applying constant exposure to color-sensitive layers be set in a desirable manner. When the constant expoure matching the photographic distribution probability of an original color picture is applied to color-sensitive layers, a rate of obtaining a highquality copied print can be increased. For example, during the summer, in which scenes at beaches and outside houses are photographed frequently, the exposure, which is controlled to a constant level as mentioned above, is set to a lower level, and when indoor scenes are photographed, frequently with a flashlight, the standard copying conditions are set so as to maintain the exposure at a higher level. This allows the rate of making high-quality copied prints to be increased.
The film manufacturers and some photo finishers provide or make original color pictures for use in setting standard copying conditions and object copied prints are based on the original color pictures with reference to the statistic and experiential photographing distribution of original color pictures. In a color printer, an original color picture (which will be hereinafter referred to as a setup patch in this specification) for setting the standard copying conditions is used to set the standard exposure, i.e., the standard copying conditions for the exposure a color printer to form an object copied print. This is called setup.
The setup has a great influence upon the quality of a copied print, and a great deal of effort has been concentrated upon this point in color copying techniques. Unless the setup in done excellently, the exposure controlling conditions are not established. This causes the rate of obtaining high-quality copied prints and the productivity of copied prints to be decreased greatly, and the cost of production of copied prints to be increased greatly.
The setup is usually done in such a manner that an operator copies a setup patch repeatedly on trial while varying the exposure, to make a copied print approximating an object copied print and define the exposure, at which a copied print approximating an object copied print is made, as a standard exposure. However, in this method, much time and money are required to copy a setup patch on trial and an operator having the skill of judging copied prints visually.
There is a color printer provided with a computer and a means for measuring the density of an object copied print in advance with a reflection densitometer, storing the result of measurement in a memory, measuring the density of a copied print obtained by copying a setup patch on trial for determining a standard copying condition, manually inputting the density thus measured, computing the exposure, at which an object copied print can be obtained, by using a linear equation representing the difference between the manually inputted amount of measurement and the density measured as mentioned above of an object copied print, and setting the resulting exposure as a standard exposure. However, this printer requires an expensive reflection densitometer and also much time to carry out a inputting operation. Moreover, the linear equation is not established in many cases due to manufacturing or adjusting errors of the reflection densitometer and the irregularity of the photosensitive characteristics of different lots of photosensitive copying medium. Consequently, the above printer does not necessarily permit accurately setting a standard exposure.
An exposure control in a color printer usually depends upon the quality of the light from a copying light source. Therefore, when any change occurs between the quality of the light from a copying light source used for copying a setup patch and that of the light from a copying light source used for setting the standard copying conditions, the exposure cannot necessarily be controlled in a desired manner. However, when the constant exposure is not obtained suitably, the exposure controlling conditions referred to above are not established. Consequently, it becomes very difficult to obtain a high-quality copied print.
The exposure referred to above of each color means that an amount of transmitted light, which is obtained by integrating an amount of transmitted light with respect to an original color picture on the basis of the exposure time, contributes to the sensing of light in blue, green and red photosensitive layers of a photosensitive copying medium (mainly color paper). The above integrated amount is usually controlled so as to be maintained at a constant level on the basis of the relative relation between actual amounts of blue, green and red transmitted light concerned with the color printer and the amount of light referred to above. (The exposure to be referred to in the later paragraphs shall mean the integrated amount referred to above unless otherwise specified).
The constant amount referred to above of transmitted light of each color is determined in a condition-setting process. The conditions are generally set in a process for copying the standard original picture repeatedly on trial by using a standard original picture having an average transmission density, which is statistically and experientially determined, of an average original color picture while varying the exposure; and then defining as a standard exposure the exposure, which permits giving a predetermined object density to the copied prints thus obtained, and which is concerned with the color printer. This process is carried out in accordance with the sensitivity of a photosensitive copying medium, for each medium (mainly a color film) to be copied. The expense and time required for copying a standard original picture in this process vary in accordance with the skill of the operators. Even a skilled operator requires a considerable amount of expense and a considerably long time for carrying out the process. In addition, in order to make high-quality prints, it is necessary to set these conditions excellently.
It is also an essential condition for stably making high-quality copied prints that the exposure, which is defined in the conditions set as excellent copying conditions, and which corresponds to the standard exposure concerned with the color printer, be constantly maintained. Unless these conditions are satisfied, it is difficult to make high-quality copied prints.
However, it is a common phenomenon in a copying operation that the exposure corresponding to the standard exposure concerned with the color printer is not maintained at a constant level but varies unnecessarily. As mentioned previously, the exposure is controlled on the basis of the relative relation between amounts of transmitted light contributing to the sensing of the light in the photosensitive layers of various colors of a photosensitive copying medium and actual amounts of transmitted light of various colors concerned with the color printer. However, the amounts of transmitted light in a photosensitive copying medium and those of transmitted light concerned with the color printer do not generally agree with one another. This is ascribed to the difference between the spectral sensitivities of the blue, green and red photosensitive layers of a photosensitive copying medium and those of light detectors used in a color printer to determine the amounts of blue, green and red transmitted light. During a copying operation, the transmitted light in an original color picture usually varies due to the variations in the quality of the light from a copying light source, or variations in an average transmission density of the original color picture, or a combination of these variations. Due to the variations in the transmitted light in an original color picture in addition to the above-mentioned disagreement between the amounts of transmitted light in a photosensitive copying medium and those of transmitted light concerned with the color printer, the exposure cannot be controlled to an object level. Therefore, the exposure cannot be maintained at a constant level.
There is a known example, in which a filter adapted to absorb the light in low-sensitivity wavelength regions in each color sensitive layer of a photosensitive copying medium is inserted in the portion of a copying optical path which is between a copying light source and light detectors similar to the one referred to above, to properly establish the above-mentioned relative relation between amounts of transmitted light in a photosensitive copying medium and those of transmitted light concerned with the color printer. In this example, the difference between the spectral sensitivities of the photosensitive layers of a photosensitive copying medium and those of light detectors cannot be eliminated, so that an object effect cannot be obtained.
A conventional color printer also has a means for correcting actual amounts of blue, green and red transmitted light with the functions thereof. This correcting means is used mainly for approximately normalizing variations in an amount of transmitted light, which contributes to the sensing of the light in each color-sensitive layer of a photosensitive medium, on the basis of variations in an actual amount of the transmitted light due to variations in an average transmission density of an original color picture. This correcting means serves to obtain high-quality copied prints provided that the quality of the light from a copying light source does not vary. However, variations in an average transmission density of an original color picture and variations in the spectral intensity in the transmitted light, which are due to the variations in the quality of the light from a copying light source, are different. Accordingly, when the quality of the light from the copying light source varies, it is difficult to normalize as mentioned above by the above-mentioned correcting means the variations in an actual amount of the transmitted light, which occur due to variations in the transmitted light including the variations in the quality of the light from the copying light source. In addition, unnecessary variations occur in the exposure, so that high-quality copied prints cannot necessarily be made.
Variations in the quality of the light from a copying light source occur mainly in the following cases. A first case is a case, which accompanies with variations in the properties of a light source lamp used as a copying light source. It is difficult to maintain the quality of the light from a light source lamp at a constant level during a long-term use thereof. When a light source lamp is renewed due to the termination of the life thereof, the quality of the light from a new light source lamp is usually different from that of the old light source lamp. In the case where the light from a light source lamp is regulated by the lighting voltage therefor, the quality of the light also varies in the same manner as mentioned above. A second case is a case where the properties of the light from a light source vary while the light is regulated by color compensating filters. The exposure of, especially, blue, green and red is controlled with cut filters and a shutter. In a color printer, the light is regulated mostly for the purpose of setting substantially identical the time for operating cut filters and the time for operating a shutter, with respect to an average original color picture in accordance with the standard exposure, which is defined in the set conditions, and which is concerned with the color printer. The purpose of setting the operation time of cut filters and that of a shutter substantially identical with each other is to improve the production efficiency of copied prints, and obtain in some types of color printers the color correcting effect by incorrectly absorbing the colors, which are other than the main colors to be absorbed in the cut filters.
As described above, variations in the quality of the light from a copying light source occur not only when the light is regulated by an operator but also accidentally at any time. In order to eliminate in a conventional color printer the influence of unnecessary fluctuations of the exposure, which is caused by variations in the quality of the light from a copying light source, there is no better way than to set suitable conditions by using more money and sparing more time. Unless the influence referred to above is eliminated, high-quality copied prints cannot be constantly made.